The present invention relates to a reader/writer transmitting and receiving data to and from a wireless tag through wireless communications, and relates to a data communication method performed between the wireless tag and the reader/writer.
In the case of transmitting and receiving the data batchwise such as reading and writing the data to and from a plurality of wireless tags existing in a communication-enabled range of a reader/writer capable of performing the wireless communications with a passive type of wireless tag, collision with other wireless tags is avoided by such a scheme that there be always one combination of a single communication-enabled wireless tag and the reader/writer (refer to, e.g., Non-patent documents 1 and 2). In these collision avoidance techniques, the wireless tag undergoing completion of a data transmitting/receiving process by the reader/writer is temporarily stored with a flag representing this completion status (which will hereinafter be referred to as a [completion flag]). This completion flag is designed to be retained for approximately 2 through 5 seconds by utilizing electric power accumulated in a capacitor etc within the wireless tag even if the power supply from the reader/writer is cut off.
Accordingly, the reader/writer is capable of distinguishing between the wireless tag undergoing the completion of the process by the reader/writer and the wireless tag not yet subjected to the process during the period for which to retain this completion flag. As a result, this enables the reader/writer to efficiently perform the data communications with the plurality of wireless tags.
[Non-patent document 1] ISO/IEC 18000-6 Type B (Chapter 8.2.5)
[Non-patent document 2] ISO/IEC 18000-6 Type C (Chapters 6.3.2.6-6.3.2.9)